1. Field of the Invention
The present invention is directed to a wavefront measuring device, and more specifically, to wavefront sensor for measuring ocular aberrations.
2. Description of the Related Art
Ocular aberrations are typically the result of variations in the eye's lens and cornea which preclude the points on an object from uniformly coming to a sharp focus on the retina of the eye. Various refractive techniques have been used to correct ocular aberrations, such as the external eye glasses or contact lenses. For such corrective methods, interaction by the patent is generally available to the practitioner for determining the appropriate level of correction. Once the required amounts of spherical and cylindrical correction are determined, corrective lenses are made to restore visual acuity. In recent years, the field of ophthalmology has also developed more advanced techniques, such as Photorefractive Keratectomy (PRK), Laser Epithelial Keratomileusis (LASEK), and Laser-Assisted In-Situ Keratomileusis (LASIK), which allow the practitioner to directly modify the shape of the cornea to restore visual acuity.
Eye glasses and contact lenses generally correct only for ocular defocus and astigmatism. A wavefront sensor is a device that allows characterization of a wavefront in order to determine deviations in the wavefront from an idealized wavefront profile. The use of wavefront sensors offers the possibility of identifying and correcting additional ocular aberrations such as coma, sphere, and other higher order aberrations. Using a wavefront sensors also allows the practitioner to objectively quantify the amount of ocular aberrations without patient interaction.
In one approach, a Shack-Hartmann type wavefront sensor is used to measure ocular aberrations by first focusing light onto the retina by using the eye's own cornea and lens. The focused spot on the eye acts as a point source that illuminates the lens and cornea from behind to produce a wavefront that may be examined using the wavefront sensor to measure ocular aberrations. The Shack-Hartmann wavefront sensors are commonly used to measure ocular aberrations, since such sensors do not require a coherent light source and is, therefore, robust to vibrations. Other benefits of the Shack-Hartmann sensor in ocular applications include (1) the measurement is typically very fast because single frame includes all the information needed to calculate wavefront aberration and (2) measurement performance is not sensitive to other system aberrations since these aberrations can calibrated out by using reference spot array pattern.
A typical Shack-Hartmann wavefront sensor based device for ocular applications is disclosed by Williams and the present inventor in U.S. Pat. No. 6,264,328, which is hereby incorporated by reference. Using the device disclosed by Williams et. al., light from a light source is focused onto the retina of an eye. Light reflected by the retina passes back through the lens and cornea of the eye produces an aberrated wavefront in front of the eye. A pair of imaging lenses are used to transfer an image of the wavefront to a Shack-Hartman or equivalent wavefront sensor using the pair of lenses. There exist a need to reduce the size and increase the durability in this and similar types of instruments used in the measurement of ocular wavefronts.